Medical containers comprising a stopper in gliding engagement within a barrel are widely used to deliver drug to patients.
Such containers include syringes, cartridges and auto-injectors.
They are preferably prefilled in order to be more easily used by a patient or by medical staff, and to eliminate the risk of contamination that occurs when a drug is transferred from a vial to an injection device.
Such medical containers are usually lubricated to ensure a good gliding movement of the stopper within the barrel when the drug is injected to a patient.
The gliding movement of the stopper involves the application of an activation force to put the stopper in motion, then of a gliding force to maintain the motion of the stopper.
In order to have a smooth gliding and to avoid any stick-slip effect, the activation force and gliding force have to be as low as possible.
Lubricant may consist in mineral or vegetable oil or in a synthetic lubricant.
Silicone oil such as poly-(dimethylsiloxane) is widely used as lubricant for such applications.
However, such silicone oil has the drawback of being unstable over time and especially after autoclave treatments that are usually performed to ensure the sterility of the medical container, before or after the filling of the medical containers with pharmaceutical compositions.
Due to ageing or to such treatments, it is common to observe squeeze-out of the lubricant under the pressure exerted between the stopper and the barrel.
However, if the lubricant squeezes-out i.e. migrates from the interface between the stopper and the barrel, the activation force of the stopper becomes higher and does not allow for a smooth gliding of the stopper.
The accuracy of the delivered dose of a pharmaceutical solution contained into the medical container is therefore decreased particularly when the injection is performed by a pump.
Document EP 0 920 879 proposes a lubricant composition consisting of a mixture of non-reactive silicone oil and reactive silicone, namely a vinyl-based silicone, with a fraction of non-reactive silicone in the mixture comprised between 5 and 85% by weight.
The composition is then applied to a medical container and subjected to a cross-linking treatment.
As a result, the coating forms a solid film along the inner wall of the barrel.
However, such a coating still presents poor mechanical performances, i.e. high activation and gliding forces.
In particular, the activation force remains higher than the maximum desired limit.